Radioactive tracers

Introduction

Transportation, whether in plants or animals is the key to the efficient assimilation of the nutrients that the organisms synthesise, get from their environment or digest. The study of these processes helps us in many ways.

The study of transport mechanisms in plants helps us to understand the uptake of the various types of substances and their passage through the plants. This has helped a great deal in developing fungicides, pesticides, growth regulators, etc. and how they should be administered to the plants.

In animals too the study of transport has helped us in diagnosing disease and in developing new and more effective drugs and treatments.
Taken from: http://www.tutorvista.com/content/science/science-ii/transportation/introduction.php

An important technique used to study transport in both animals and plants, used in a multitude of applications, is the use of radioactive tracers.

Radioactive isotopes

Isotopes are atoms of the same elements which contain the same number of protons but different number of neutrons (eg. Carbon-12 has 6 neutrons, while Carbon-14 has 8 neutrons). Radioactive isotopes are isotopes which are unstable (that is, their nucleus does not hold together well and therefore breaks down, making the compound radioactive) and undergoes radioactive decay while emitting heat and radiation.
Taken from: http://scienceray.com/philosophy-of-science/radioactive-substances-and-its-uses/

There are many practical applications to the use of radioactivity/radiation. Radioactive isotopes (aka radio-isotopes) are used to study living organisms, to diagnose and treat diseases, to sterilize medical instruments and food, to produce energy for heat and electric power, and to monitor various steps in all types of industrial processes.

Tracers

Tracers are a common application of radio-isotopes. A tracer is a radioactive isotope of an element whose pathway through which a chemical reaction can be followed. Tracers are commonly used in the medical field and in the study of plants and animals.
Taken from: http://www.ndt-ed.org/EducationResources/HighSchool/Radiography/usesradioactivity.htm

Using isotopes as tracers

Radioactive isotopes have many useful applications in a wide variety of situations, for example, they can be used within a plant or animal to follow the movement of certain chemicals. In medicine, they have many uses, such as imaging, being used as tracers to identify abnormal bodily processes, testing of new drugs and conducting research into cures for disease.

Phosphorus uptake by plants

Plants take up phosphorus-containing compounds from the soil through their roots. By adding a small amount of radioactive phosphorus-32 to fertiliser and then measuring the rate at which radioactivity appears in the leaves, it is possible to calculate the rate of uptake of phosphorus from the soil. The information gathered could help plant biologists to identify plant types that can absorb phosphorus quickly. These plants may give better yields resulting in more food or fibre at less expense.

Carbon-14 was used by Melvin Calvin (after whom the Calvin cycle is named) to map the path of carbon in photosynthesis and for which he won the Nobel Prize in 1961. It is useful as a radioactive tracer in plants as carbon is taken in by the plant in the form of carbon dioxide and is then incorporated into the carbon containing compound, glucose, and other carbohydrates (eg. starch).

Pesticide levels

To measure pesticide levels, a pesticide can be tagged with a radioisotope such as chlorine-36, and this is applied to a field of test plants. Over a period of time, radioactivity measurements are made. Estimates can then be made about how much accumulates in the soil, how much is taken up by the plant and how much is carried off in run-off surface water.

Medical tracers

Radioactive isotopes and radioactively labelled molecules are used as tracers to